1. Field of the Invention
The present invention relates to a light-emitting diode, and more particularly to a light-emitting diode in which a diffusion layer formed using a diffusion mask is formed into a diffusion region by the selective diffusion of an impurity metal.
2. Description of the Prior Art
The light, small light-emitting diode (LED) is extensively utilized in various fields. In recent years the merits of the LED have been utilized to realize practical LED printers and other such devices, and various other applications are being proposed in which LEDs are used as a light source.
FIG. 2 is a cross-sectional view of a typical conventional light-emitting diode. With reference to FIG. 2, an n-GaAsP layer (hereinafter "n-layer") 12 formed on an n-GaAs substrate (hereinafter 37 substrate") 10, and then formed on the n-layer 12 is a diffusion mask layer 14 that is constituted of a substance such as SiN and provided with an opening 14A of a prescribed pattern. Zinc or other such impurity element is diffused into the n-layer 12 through the diffusion mask layer opening 14A, thereby forming a p-diffusion region 18. A p-electrode 20 constituted of gold or other such substance is formed on the p-diffusion region 18 and an n-electrode 22 on the under-surface of the substrate 10. Reference numeral 16 denotes a surface protective layer of SiN or the like.
In the conventional LED thus configured, the application of a voltage across the p-electrode 20 and n-electrode 22 sets up a flow of current that stimulates the emission of light in the area of the junction formed by the n-layer 12 and p-diffusion region 18, and this light is directed upward through the protective layer 16. This protective layer 16 is usually constituted so as not to reflect light from the diffusion region 18.
However, a drawback with this type of conventional LED is that in the diffusion process the p-diffusion region 18 expands laterally and wraps around under the diffusion mask layer, and light emitted from this peripheral wraparound portion of the junction is therefore attenuated by the diffusion mask layer located above, adversely affecting emission efficiency. A further problem is that as the light intensity at the peripheral portions is lower than at the center of the p-diffusion region 18, the light output distribution in the emission plane is not uniform.